Just to clear up the extra cover 'thing', I was referring to the ebay satchels.

If you take your click & send satchel to the PO it will be scanned into the system and will show up on the AP tracking in the majority of cases, you also get a receipt. If you post straight into the box they will not be scanned until further into the system and if it goes missing and does not get tracked to the delivery address you have no proof that it was posted, just that you paid for the postage through the click & send site.